How to edit two objects in edit mode?
Install this addon

After installation you can find this addon in toolshelf -> tools -> multi object editing



How to use

Go to toolshelf -> tools -> multi object editing and Click on Enable Multi Edit mode

Select the objects that you need to edit same time.

Now go to toolshelf -> tools -> multi object editing and select Multiedit enter as soon as you click your are in edit mode and now you can edit the mesh which you have selected before.

After editing Press Tab to be in object mode. When you click the objects look join to separate them. 

Go to toolshelf -> tools -> multi object editing and select Multiedit exit